The present invention relates to star or radial polymers having a plurality of long polymeric arms radiating from a nucleus. The invention also relates to a novel process for the preparation of the star polymers described herein.
Star or radial copolymers are generally known and have been utilized as adhesives and in the thermoplastics industry. Such polymers have been prepared by polymerization of a monomer A, with an organolithium compound followed by the addition of another monomer B, to form an AB block copolymer terminated by a lithium ion. Subsequently, a polyfunctional linking agent is added to the lithium terminated AB blocks to form the star or radial structure which consists of the copolymeric arms connected to the linking agent, the linking agent being in such a small proportion to the total weight percent of the resulting copolymer that its presence is relatively inconsequential as compared to the properties of the polymeric constituents.
Many linking agents are available and generally it has been taught that the number of arms formed is dependent upon the number of functional groups carried by the linking agent. Thus, utilizing a di-halo hydrocarbon such as 1,2-dibromoethane, as taught by U.S. Pat. No. 3,507,934, one could prepare an ABA triblock copolymer from the coupling of two AB diblocks. Di and trivinyl aromatic compounds have been used to prepare a difunctional initiator and from that block copolymers of the ABA type have been made as taught by U.S. Pat. No. 3,644,322. Tetrafunctional tin compounds such as tetrallyltin and stannic fluoride may also be selected as disclosed in U.S. Pat. No. 3,639,517 to combine four polymeric arms into one molecule. However, to obtaine more than four arms, it has been thought necessary to employ a linking agent having five or more reactive sites. While such compounds may be available, little if any work has been undertaken to obtain, much less study, star polymers having more than four polymeric arms.
Although it has been stated in U.S. Pat. No. 3,639,517, that some monomeric materials may be employed as the linking agent, it was there noted that one could obtain a branched block copolymer but not a radial polymer by such means. Regardless of the linking agent selected or the process by which star polymers have been made, it has not been readily possible heretofore to obtain a polymer having more than four arms and a high molecular weight, e.g., 300,000 and higher, with a relatively low viscosity. As is readily recognized in the art, such molecular weight ranges in linear copolymers, random branched or unbranched, have almost prohibitive viscosities making them unsuitable for most purposes.